Field of the Invention
This invention pertains to semiconductor devices and, more particularly, to a method and apparatus for applying adhesively coated tape material segments, i.e., decals, to leadframes for semiconductor devices, particularly including Lead-Over-Chip type semiconductor device assemblies.
State of the Art
In semiconductor manufacture, a single semiconductor die (or chip) typically has a lower surface, the back of the die, being devoid of circuitry located thereon. Each semiconductor die also has an opposite upper surface, the active surface or face of the die, having integrated circuitry constructed thereon which is electrically accessible via wire bonding pads located thereon. The wire bonding pads may be arranged in a variety of configurations on the active surface of the semiconductor device, such as along the center of the die, the edges of the die, both, etc.
Typically, a leadframe is used to connect the wire bonding pads of the semiconductor device via wire bonds to other electronic circuitry.
A conventional leadframe and semiconductor device assembly or packaging process employs an adhesive layer to attach the semiconductor device to the die paddle of the leadframe while the lead fingers of the leadframe extend to and terminate adjacent the peripheral edges of the semiconductor device. Typically, the adhesive used to attach the semiconductor device to the die paddle is an epoxy acrylic silicone of polyamide material.
Alternatively, a lead-over chip, also sometimes referred to as a lead-on-chip (LOC), leadframe is used to provide lead fingers to be electrically connected to the bond pads of the semiconductor device through wire bonds thereto and to support the semiconductor device by being adhesively secured to the active surface thereof and, subsequently, encapsulated. An LOC type semiconductor package is described in U.S. Pat. No. 4,862,245 (Pashby et al.).
Typically, in an LOC semiconductor device assembly, the active surface of the semiconductor device is adhesively attached to the underside of the lead fingers of the leadframe through the use of a double-sided, adhesively coated tape having a thermosetting adhesive thereon, although a thermoplastic adhesive may also be used if desired. That is, the adhesively coated tape has thermosetting adhesive coated on both sides thereof and is attached to the underside of the leadframe fingers and the active surface of the semiconductor device using heat and pressure. If necessary, an oven may then be used to further cure the adhesive. After the adhesive is cured, securing the lead fingers in position on the active surface of the semiconductor device, the leadframe is transferred to a wire bonding machine where the bond wires are connected to the bond pads on the active surface of the semiconductor device and to the lead fingers of the leadframe.
Prior to attaching the semiconductor device to the leadframe using an LOC configuration, the adhesively coated tape must be placed onto a heated leadframe that will secure the semiconductor device to the leadframe but will allow access to the bond pads of the semiconductor device. Typically, a single piece of LOC tape is distanced from a continuous roll of tape and cut, using a punch, into two tape segments, i.e., decals, that are spaced apart and cut away to provide access to the bond pads of the semiconductor device. In such an LOC configuration, the continuous strip of leadframes to which the adhesively coated tape is to be applied at die sites thereon is moved perpendicularly to the direction of feeding of the continuous roll of tape from which the tape is cut and applied to the die sites of the leadframe. In such an instance, a single punch is typically used to cut the tape from the continuous roll of tape and apply the cut tape to the die site of an individual leadframe in a one-punch operation where the tape is fed orthogonally with respect to the feeding and movement of the leadframes. The leads of the die site of the leadframe to which tape is applied by the punch are, in turn, positioned such that the tape segments are located adjacent each other on the leads of the leadframe at the die site, such leads extending orthogonally on the leadframe with respect to the movement of the leadframe through the punch assembly.
Such a process suffers from the problem that LOC tape is an expensive material and a large amount of tape is wasted during formation of the LOC tape pieces. With a conventional LOC tape punching apparatus as described hereinbefore, the width of the tape must be large enough to punch two pieces of tape with a space therebetween for the bond pads of the semiconductor device. Therefore, typically, the pieces of tape are cut from the center of a continuous length of tape having a width that is larger than required for the individual pieces of tape. Additionally, the tape cut out for the area where the bond pads of the semiconductor device are located is also waste. In some prior art systems, as much as seventy-five percent (75%) of the tape may be wasted in the cutting and application of pieces of tape to a leadframe, such as an LOC leadframe.
Since adhesive tape used for the LOC type semiconductor device assembly, or any leadframe design which requires the use of tape thereon, is relatively expensive and the misapplication of the tape during the manufacturing process can produce problems in the subsequent automated manufacturing processes, in turn, imposing increased costs, a method for efficiently applying adhesive tape where desired on a leadframe is desirable. Particularly, it is desirable to have tape applied to a leadframe without wasting tape and without having to apply the tape in a single punch operation to the desired die site of the leadframe.
A system and method for applying adhesively coated tape material to the die sites of semiconductor leadframes where the die site of the leadframe is indexed to separate locations for the application of each tape segment, i.e., decal. The system and method are used to apply tape segments to leadframes having leads to which the tape segments are applied which are, in turn, parallel to the direction of movement of the leadframe through the tape die assembly, although, if desired, the leads on the leadframe may extend orthogonally with respect to the direction of movement of the leadframe and the tape segments to be applied thereto.
A system for applying adhesively coated tape material to the die sites of semiconductor leadframes includes a first source for supplying a first length of adhesively coated tape material to a first location of a die site of the leadframe and a second source for supplying a second length of adhesively coated tape material to a second location at the die site of the leadframe after the indexing of the die site of the leadframe to another location for the application of tape thereto. Indexing means are also provided to supply and index for the application of tape to a die site of a plurality of leadframes for semiconductor devices in die site by die site of a leadframe-by-leadframe sequence. An xe2x80x9capplication meansxe2x80x9d is configured to receive the plurality of leadframes for semiconductor devices in a die site by die site of a leadframe-by-leadframe sequence and to receive the first length and the second length of adhesively coated tape materials, supplied in strip form. The application means has cutting means for independently cutting a first increment from the first length of adhesively coated tape material and applying the first increment to a first portion of a die site of a leadframe of the plurality of leadframes, supplied in strip form. The cutting means of the application means also independently cuts a second increment of the second length of adhesively coated tape material and applies the second increment to a second portion of the die site of a leadframe of the plurality of leadframes. Control means are interconnected to the application means, to the indexing means, to the first source and to the second source, all supplying operation signals to the control means.
The operation signals operate the indexing means to supply a plurality of leadframes for semiconductor devices in leadframe-by-leadframe sequence to the application means and to position the first portion of the die site and the second portion of the die site to receive the first increment and the second increment of adhesively coated tape material, respectively. The operation signals are also supplied to operate the first source to cause the first length of adhesively coated tape material to be selectively supplied to the application means when or as the first site is positioned to receive the first increment at the first portion thereof. The operation signals are also provided to operate the second source to cause the second length of adhesively coated tape material to be supplied to the application means when or as the second portion of the first die site is positioned to receive the second increment. The control means also supplies operation signals to operate the cutting means of the application means to selectively cut and apply the first increment to the first portion of the die site of a leadframe of the plurality of leadframes and to cut and apply the second increment to the second portion of the die site of a leadframe of the plurality of leadframes.
In the preferred arrangement, the cutting means includes a first die movable relative to a first cutting structure configured to receive the first length of the adhesively coated tape material. The cutting means also includes operation means positioned to independently move the first die relative to the first cutting structure to form the first increment and to urge the first increment toward and against the first portion of the die site of a leadframe of a plurality of leadframes. The cutting means also preferably includes a second die independently movable relative to the second cutting structure configured to receive the second length of adhesively coated tape material. The operation means is preferably positioned to move the second die relative to the second cutting structure to form the second increment and to urge the second increment toward and against the second portion of the die site of a leadframe of the plurality of leadframes.
Desirably, the first source includes a first adhesively coated tape supply configured to supply the first length and first driving means positioned to receive the first length and to urge the first length towards the first cutting structure. The first driving means is connected to the control means to receive operation signals to urge the first length toward the first cutting structure only when a first portion of the die site of a leadframe of the plurality of leadframes is positioned or is to be positioned relative to the first portion of the die site to receive the first increment.
The second source preferably includes a second adhesively coated tape supply configured to supply the second length and second driving means positioned to receive the second length. Second driving means also operates to urge the second length toward the second cutting structure. The second driving means is connected to the control means to receive operation signals to urge the second length toward the second cutting structure only when a second portion of the die site of a leadframe of the plurality of leadframes is positioned or is to be positioned relative to the second die to receive the second increment.
Preferably, the first driving means is a first stepping motor connected to a first drive roller over which the first length of adhesively coated tape material is positioned. The first driving means may also include a first driven roller positioned proximate the first drive roller with the first length of adhesively coated tape material positioned between the first drive roller and the first driven roller. Similarly and desirably, the second driving means includes a second stepping motor connected to a second drive roller with a second driven roller positioned proximate the second drive roller. The second length of adhesively coated tape material is positioned between the second driven roller and the second drive roller.
In preferred configurations, the first driving means and the second driving means both include guide structure to guide the first length between the supply of adhesively coated tape material and the first cutting structure.
The indexing means preferably includes structure configured to urge the plurality of leadframes in strip form for semiconductor devices in leadframe-by-leadframe sequence relative to the application means. The plurality of leadframes is connected one to the other in a continuous strip form. The indexing means preferably includes a movable member which engages at least one indexing hole of at least one rail of the leadframe strip to move the leadframe the desired distance for the application of the adhesively coated tape material. The indexing means alternately includes a roller with a motor connected to drive the roller. The motor is connected to the control means to receive operation signals therefrom to cause the motor to move the plurality of leadframes relative to the application means in the leadframe-by-leadframe sequence. The plurality of leadframes preferably is formed in a continuous strip form having removable carrier rails or edges thereon having, in turn, drive perforations formed therein. The roller desirably includes a plurality of teeth positioned to drivingly engage a portion of the drive perforations to thereby connect to and drive the plurality of leadframes.
The operation means of the cutting means preferably includes a first die moving mechanism. The first die moving mechanism may be a solenoid mechanism positioned to urge the first die frame to move. The solenoid is connected to receive operation signals from the control means to cause the first die moving mechanism to move the first die toward a leadframe of a plurality of leadframes.
The application means preferably includes a block positioned opposite the first die with a leadframe of the plurality of leadframes positioned between the block and the first die. The block inhibits movement of the leadframe of the plurality of leadframes upon movement of the first die against the leadframe of a plurality of leadframes. The block is preferably sized for positioning opposite both the first die and the second die with a leadframe of the plurality of leadframes positioned between the block and the first die and with a leadframe of the plurality of leadframes positioned between the block and the second die. The block desirably includes heat means to heat the block and, in turn, the leadframe, the first increment and the second increment upon urging of the first increment and the second increment against a leadframe of the plurality of leadframes.
The application means also may include guide structure for guiding the first length of adhesively coated tape material and guide structure for guiding the second length of adhesively coated tape material. The first cutting structure and the second cutting structure may be unitarily formed into a single structure. The operation means may be desirably configured to urge the first die and the second die together. Alternatively, the operation means may be configured to urge the first die and the second die to move independent of each other.
In a desired alternative arrangement, the plurality of leadframes includes a first leadframe, a middle leadframe and a last leadframe. The indexing means is operable to urge the first leadframe to a first position with its first site positioned relative to the first die to receive the first increment upon activation of the first source with the second site positioned spaced to not be contacted by the second die. Control means is configured to send operation signals to activate the first source to supply the first length of adhesively coated tape material to the first cutting means and to send operation signals to not activate the second source.
Desirably, the indexing means is also operable to urge the middle leadframe to have its first site positioned relative to the first die to receive the first increment upon activation of the first source and the first die to thereafter urge the middle leadframe to have its second site positioned relative to the second die to receive the second increment upon activation of the second source and the second die. The control means preferably sends operation signals to activate the first source to supply the first length of adhesively coated tape material to the first cutting means and to activate the second source to supply the second length of adhesively coated tape material to the second cutting means.
Most desirably, the indexing means is operable to urge the last leadframe to be positioned with its second site positioned relative to the second die to receive the second increment upon activation of the second source and the second die. The first site is positioned to not be contacted by the first die. The operation means desirably sends operation signals (e.g., no signals) to activate the second source to supply the second length to the second cutting means and to not activate the first source. Preferably, the indexing means urges the first leadframe and the middle leadframe and the last leadframe to move continuously in sequence while simultaneously causing the first source and the second source to operate to supply the respective first length and the second length to the first cutting means and the second cutting means.
In an alternative arrangement, a system to apply adhesively coated tape to an LOC leadframe of a plurality of LOC leadframes includes a base and a block positioned opposite the base and spaced therefrom for an LOC leadframe to pass closely and freely therebetween. Supply means is positioned relative to the base to supply the first adhesively coated tape length and the second adhesively coated tape length. Indexing means are provided to move each LOC leadframe of the plurality of leadframes relative to the base. Application means is mechanically associated with the base for cutting the first tape length into a first tape decal and applying the first tape decal to a first position at a die site of the LOC leadframe. The application means also cuts the second tape length into a second tape decal and applies the second decal to a second position of the die site of the LOC leadframe. Control means are interconnected to the supply means, to the application means and to the indexing means to supply control signals so that decals are applied to the first position of a die site on an LOC leadframe and so that decals are applied to the second position of a die site on an LOC leadframe.
A method of attaching decals includes providing the first source, the second source, indexing means and application means. The method includes operating the first source to supply a length of first adhesively coated tape to the application means. The second source is also operated to supply a length of adhesively coated tape to the application means. The application means operates to cut the first decal from the first length of the first adhesively coated tape and applies the first decal to the first position of a die site of each LOC leadframe.
The application means includes a first die for cutting the first decal and a second die for cutting the second decal. The indexing means operates to advance the first LOC leadframe of the plurality of leadframes to position its first site to receive the first decal, to index the first leadframe to position its second position of a die site to receive the second decal, and to concurrently index a second LOC leadframe of the plurality of LOC leadframes to position the first site of the second LOC leadframe on the plurality of LOC leadframes to receive another first decal at the same time the first LOC leadframe is to receive the second decal.